What should I do?

For the past two years my best friend (of 8 years) and I have had a bit of a rocky relationship. It started when I asked her (admittedly in a rude why) why she didn't tell me that my boyfriend sent her a nude. (He didn't but I was told otherwise.) She and I had a blow out. After that every few months she or I would get really angry over something just as petty and quit talking for awhile.

About a year ago she started seeing a therapist. She saw him for a few months then quit because he told her that I was toxic. I promised to do better, but after 6-8 months I fell off again. She is now seeing a new therapist that advised the same. This time she blocked me on all mediums with no warning or anything.

I'm so broken. I've reached out and tried to get help. It's been three months and a massive amount of things have happened that accelerated change. I tried to tell her how much better I could do, but she wouldn't listen to me. Should I wait awhile and try again or just let go?? She means the world to me and I don't want to let go that easily. It kills me to think she could drop me and not even think twice.